Method and apparatus for deforming reformable tubular pipe liners

ABSTRACT

A method producing deformed pipe liners from continuously extruded thermoplastic material by collapsing and bending deformable portions of the tube toward a back-up portion thereof and without elongation to maintain diameter and wall thickness, and apparatus to carry out said method and characterized by at least one back-up roller and at least one shaping roller folding the deformable portion along a line of symmetry and juxtaposing a fold of the tube to the back-up portion, all at raised temperature followed by reduced temperature on a rail conforming to the deformed tube configuration.

This is a continuation of application Ser. No. 07/389,693, filed Aug. 4,1989, now abandoned, which, in turn, is a division of application Ser.No. 07/077,883, filed Jul. 27, 1987 for "Method and Apparatus forDeforming Reformable Tubular Pipe Liners," now U.S. Pat. No. 4,863,365,dated Sep. 5, 1989.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to the use of thermoplastic liners within pipelines, either initially or as a repair. In the case of new piping, theliner will protect the internal walls from deterioration, and the linercan be replaced from time to time. In the case of deteriorated ordamaged piping, the liner will restore the fluid transporting capabilityof the piping and will prevent further interior deterioration. The useof such a liner for protecting the interior of pipe is taught by Dr.Jacques Laurent in French Patent No. 2,503,622 dated October, 1982 inwhich he teaches the concept of heat transfer and deformation ofpreviously extruded cylindrical tube of thermoplastic material intoU-shape cross-section for insertion into and subsequent reshaping to itsoriginal extruded form within pipe as a protective liner. It is ageneral object of this invention to provide a method and apparatus forthe manufacture of the deformed tube product useful as pipe liners ofthe type disclosed in the Laurent patent.

In its broad sense, this method of manufacturing a deformed tube productinvolves a first step of extruding a tube cross-section as required foruse as a pipe liner, and a second step of deforming the extruded tubeinto a reduced cross-section for insertion into a pipe as a linertherefor. A feature of this method of manufacturing a tube product isthe use of thermoplastic material and its temperature control at thesuccessive stages of formation, during extrusion into its initial andsubsequent form, during its deformation, and during its return toambient usable condition. It is an object of this invention to provide amethod and apparatus for the manufacture of pipe liners in continuousdeformed lengths which are then subsequently returned to their originalunstressed extruded cross-section after insertion into the pipe to beprotected thereby. In practice, the liner configuration has an outsidediameter equal to or slightly greater than the inside diameter of thepipe to be protected, whereby the said liner is either unstressed orunder slight circumferential compression; either of which conditions isreadily accommodated by the plastic liner which relies upon thesurrounding pipe for its structural support.

The first step of this process, that is the extrusion of a tubularcross-section, is state-of-the-art. However, the second step of thisprocess, that is the deformation of the extruded tube into a reducedcross-section, is novel. It is an object of this invention to deform aninitially extruded tubular cross-section without adverse effect on itsstructural integrity, and in such a manner that its initially extrudedtubular cross-section can be restored. To this end, controlled heat isapplied to establish a softened condition of the thermoplastic materialafter its extrusion, while simultaneously applying deforming toolsthereto in order to reduce its cross-sectional configuration. When thedesired reduction is achieved, heat is withdrawn from what is thefinished product of continuous length that is then stored on spools forstorage, transport and subsequent installation.

This invention is particularly concerned with the second broad stepreferred to above, which broad step is reduced into smaller secondarysteps, so to speak. The following disclosure will concentrate primarilyupon these smaller steps with respect to the method and apparatusprovided herein to perform said steps and their functions. For example,a U-shaped reduced tubular configuration is shown and described.However, it is to be understood that a V-shaped reduced tubularconfiguration is essentially the same as the U-shape, except for itsacute angle as distinguished from roundness. Also, it is to beunderstood that other cross-sectional reductions are essentially thesame, whether they be H-shaped or X-shaped, or the like; the H-shapebeing two U's round to round, and the X-shape being four V's angle toangle. The U-shape, or V-shape, is presently considered to be the mostpractical and preferred configuration for such a tube product.

In carrying out this invention, the deformation of the initiallyextruded tube, preferably of cylinder form, progresses in a gradualmanner, by shaping means. That is, at least one side of the tubularextrusion is increasingly depressed so as to condition the tubularextrusion for its lateral collapse into a reduced U-shaped, or V-shaped,cross-sectional form; thus providing a deformed tube. As pointed outabove, the aforesaid deformation is conducted in the presence ofcontrolled heat substantially below fluidity of the thermoplasticmaterial and such that such plastic is deformed without adverselyaffecting its structural integrity, whether in its deformed condition orin its subsequently re-established initial condition. It is an object ofthis invention to provide shaping means, preferably in the form ofrollers, to deform the initially extruded tube as stated. In practice,the deformation is gradual, step-by-step, utilizing combined pairs ofopposed shaping rollers. A feature is the lateral collapse of thetubular extrusion over a forming rail, by means of opposed shapingrollers that embrace such forming rail. The finished product is thencooled to ambient temperature during and/or upon its delivery from theforming rail, as by means of a cooling trough. Heating and cooling is bymeans of heat absorption or radiant heating, and preferably bytemperature controlled water baths or spray.

The present-day commercial demand for this pipe liner is a productranging from 2 inches to 24 inches in diameter. The wall thickness willvary in proportion to diameter as circumstances require, depending uponthe application involving internal pressure applied in use and strengthrequired thereby. Accordingly, there will be variations in the processsteps involving the plurality of shaping means disclosed herein asshaping rollers and back-up roller, whereby at least one side of thetubular extrusion is deformed as required. That is, the number ofshaping means and the step-by-step degree of deformation is variable,depending upon the size and wall thickness and material to be deformed.A feature of this method and apparatus is that the product is pulled outof the extruder and from the deforming tool, for delivery to a storagespool, in a controlled manner, whereby the cross-sectional configurationof the deformed tube product is uniform and within specified dimensionaltolerance. With respect to variations in size and tolerances, andespecially with respect to larger diameter pipe liners, it is an objectof this invention to provide pulling traction on the tube during itsprocess of deformation, and applied to the shaping means, disclosedherein as powered rollers. In practice, torque is independently appliedto the shaping and back-up rollers, so as to ensure uniform advance ofthe deforming tube product.

The product herein disclosed is a thermoplastic pipe liner that isreduced from its initially extruded cross-section so that it can beeasily pulled inside a pipe line and then restored to its initiallyextruded cross-section. Assuming pipe to be round in cross-section, theoutside diameter of the initially extruded and/or reformed liner tube isthe same or slightly greater than the inside diameter of the pipe thatreceives it, so that the liner exterior comes into perfect interfacecontact with the pipe interior and preferably under slightcircumferential compression. This interface contact of liner within thepipe eliminates any annulus, and so that the requirement of filling suchan annulus is virtually eliminated. A feature of this liner is itsthin-wall configuration made of a thermoplastic such as polyethylene,nylon, Teflon™, ABS, or any other such plastic material, whereby thesmall loss of inside diameter of the flow passage is largely compensatedfor by the exceptional flow coefficient within the liner made of such athermoplastic material. For new pipe line projects, extensive pipematerials such as stainless alloys can be substituted with ordinarysteel pipe, and lined with this product liner, thereby realizing a costsaving of 1.5 to 2.2, together with the improved fluid toleranceproperties of the plastic which can be selected to best advantage.Accordingly, pipe lines which are structurally sound need not bereplaced, since this product liner can be installed and replaced ascircumstances require.

The method and apparatus herein disclosed for the manufacture of thisproduct liner involves the primary step of extruding thermoplastictubing, and the secondary step of deforming the thermoplastic tubing.The primary step of extrusion involves generally, an extruder thatreceives raw plastic material and delivers a tubular cross-sectionthrough a vacuum trough that controls the processing temperature andprecise configuration of the tubular cross-section. The secondary stepof deforming the precise tubular cross-section involves generally, amulti-stage shaping tool that deforms the extrusion at controlledtemperature and delivers it through a cooling trough as the finishedproduct liner. The finished product liner is drawn from the secondarystep by a puller that controls the linear speed of the production andmaintains a constant wall thickness of the finished product liner.

These and further objects and advantages of the present invention willbecome more apparent upon reference to the following specification,appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a block diagram illustrating the method of producing anextruded plastic pipe liner for restoration to its initially extrudedcross-sectional configuration;

FIGS. 2a, 2b, 2c, 2d and 2e are sectional views of the extruded pipeliner in its sequential stages of deformation, and showing in phantomline the cylindrical configuration of the finished liner for comparisonof the deformation in each figure;

FIG. 3 is an enlarged longitudinal sectional view of the deformerapparatus which performs the method herein disclosed to deform extrudedthermoplastic tubing; and

FIGS. 4 through 9 are enlarged detailed sectional views takensubstantially as indicated by lines 4--4, 5--5, 6--6, 7--7, 8--8 and9--9 in FIG. 3.

DETAILED DESCRIPTION OF THE DRAWING FIGURES

Reference will now be made in detail to the present preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings.

Referring now to the drawings, this invention is concerned with liningnew and old pipe lines with a deformed tube that is pulled into the pipeline and then reformed to tightly fit therein. The tube can be made ofany suitable material which will collapse and subsequently return to itsoriginal cross-section, and such a material is thermosetting plastic andwithin the subject matter of the aforementioned Laurent patent. Inpractice, the pipe liner is a thin-walled plastic sleeve extruded incontinuous lengths and later inserted into pipe lines for internalprotection, and for example to protect new pipe lines and toreconstitute deteriorated pipe lines as well.

Accordingly, the pipe liner L as it is disclosed herein is initiallyextruded so as to have an exterior diameter at least as large as theinterior diameter of the pipe into which it is to be inserted, andpreferably slightly in excess of said pipe diameter in order that thetubular pipe liner L is under slight circumferential compression when itis in operating position in the pipe line. A feature of this inventionis the deformation of the tubular pipe liner L, to decrease itscross-section configuration for storage and to facilitate its insertioninto a pipe line. That is, the original cylinder cross-section of thepipe liner L is collapsed and later restored, all without destroying itsdimensional properties. Therefore, the circular configuration of thepipe liner L is not stretched, even though the material is plastic andsubject to flow. In other words, the original cylindrical cross-sectionproperties of the initially extruded pipe liner L is preserved in adeformed condition thereof which enables its insertion into pipe linesand for its subsequent reformation into its original cylindricalcross-section. The characteristic feature of this invention is that theinitially extruded thermoplastic pipe liner L is collapsed and therebydeformed without elongation, whereby its dimensional propertiesnecessary for restoration are retained.

Referring now to the deformation of pipe liner L as shown in FIGS. 2athrough 2e of the drawings, the initially extruded configuration iscylindrical, having inner and outer diameter walls 10 and 11. As shown,there is an upper back-up section 12 and a lower deformable section 13.The deformation is bilaterally symmetrical and disposed about a verticalplane a of symmetry and about which the tube formation is collapsed bymeans of bending and folding. Accordingly, there are opposite sidesections 14 and 15 which are established by center fold 16 that invertsthe lower deformable section 13 upwardly into juxtaposed relation to theinside diameter 10 of the back-up section 12. Therefore, each sidesection is comprised of a side wall depending from top dead center ofthe tube form and bent inwardly so as to continue upwardly to the centerfold 16. It is significant that the two side sections 14 and 15 arethereby collapsed into double-wall configurations which are furthercollapsed inwardly toward the center plane a of symmetry as clearlyshown in FIG. 2e which is the desired product formation.

Referring now to FIG. 1 of the drawings, the entire method of tubeformation and deformation is illustrated in its general form. As shown,there is an extruder means E followed by a cooling means C1 thatdelivers the tube form into a deformer apparatus D which performs theproduct deformation process. Following the deformation process, theproduct is then delivered through cooling means C2 so as to establish itat ambient temperature for delivery through a puller means P and onto astorage spool S or the like. The extruder means E is state-of-the-artand receives the raw thermoplastic material and forces it through anextrusion die 17 at, for example, 250° to 300° F. using heating means 18to attain that temperature. The cooling means C1 is state-of-the-art,and preferably a vacuum cooling means supported by a vacuum cooling unit19 and reducing the tube form temperature to, for example, 160° F. Thedeformer apparatus D is subjected to heat control means H that maintainsthe desired deformation temperature of, for example, 160° F. The coolingmeans C2 is state-of-the-art and reduces the tube form temperature toambient, and it is supported, for example, by a cooling tower 20 or thelike. The means C1 and C2 include pump means for water recirculation,and it is to be understood that the aforementioned temperatures can varyas circumstances require. And, the puller means P is alsostate-of-the-art and draws the finished deformed tube product from thepreceding apparatus, its pulling force being controlled so as not tostretch or compress the tube form in the process of its deformation, andthereby controlling its wall thickness.

Referring now to the method or process of deforming a continuouslyextruded tube form of plastic material, the steps thereof aresequentially as follows: firstly, a cylindrical tube form is extruded asshown by phantom lines in FIGS. 2a through 2e, thereby established auniform wall section, and preferably of cylindrical configuration. Thetop semi-circular portion, namely the back-up section 12, is supportedand the fold 16 is impressed at bottom dead center of the tube form inalignment with the center plane of symmetry and progressing upwardly andinto juxtaposed relation to the inside wall 10 of the tube form at topdead center thereof. In this process of deformation the opposite sidesections 14 and 15 are turned and/or bent inwardly at their lowerextremities 21 and 22, so that the walls thereof continue upwardlywithin their respective inside walls 10 and to the fold 16 (see FIGS. 2athrough 2d).

The fold 16 is formed by bending the tube form inwardly at bottom deadcenter thereof for collapse along the center plane of symmetry.Simultaneously with this collapse the lower extremities 21 and 22 of theside sections 14 and 15 are also inwardly bent as above described. Inpractice, collapse of the tube form is preferred in a multiplicity ofsteps, in order to conform gradually to the changing configuration ofthe tube form and without elongation of its cross-sectionalconfiguration. However, it is to be understood that collapse as thus fardescribed can be accomplished in a single step, for example, in smalldiameter tubing. As shown, however, there are four steps of collapsealong the center line a of symmetry, and each of which has back-upagainst the top section 12, it being the bottom section 13 that isdeformed.

The first step of collapse shown in FIG. 2a initiates the fold 16 bybending and commences to bend the lower extremities 21 and 22. Thesucceeding three steps of FIGS. 2b and 2c and 2d progressively andincreasingly bend and move the fold 16 closer to the inside wall 10 atthe top dead center of the tube form and simultaneously increasingly andprogressively bend and move the lower extremities 21 and 22 upwardly asshown. Thus, the tubular cross-section is reduced in its sectionalconfiguration.

Referring now to FIG. 2e of the drawings, a final step of collapse isperformed by bending the opposite side sections 14 and 15 inwardlytoward the center plane of symmetry, in order to reduce the arcuateconfiguration of said two side sections and so that they occur withinthe radius or outside diameter of the initial tube form, and so as toclear within the inside diameter of the pipe line into which theultimate pipe liner L is inserted. A feature of this final collapsingstep is bringing together the two lower extremities 21 and 22 intojuxtaposed relation to the center plane of symmetry, and preferablycloser together than the continuing tube walls upstanding therefrom tothe bends of fold 16.

Referring now to the preferred form of apparatus for deforming acontinuously extruded tube form of plastic material, see FIG. 3 and thefollowing sectional views FIGS. 4 through 9. It will be observed thatthere are five collapsing steps performed thereby, four incrementallyprogressive steps of folding the bottom section 13 of the tube formupwardly along the center plane of symmetry, and a fifth step oflaterally inward collapse. Each and all of these five steps involvesbending, and is essentially if not completely devoid of stretching orelongation of the tube wall of the pipe liner L, in its transversecross-section. Each step of collapse is performed by forming means,preferably in the form of shaping rollers R1, R2, R3 and R4, followed byshaping rollers S1 and S2. It is these rollers which increasingly andprogressively collapse the extruded tube form. In practice, the shapingrollers R1-R4 are lowermost, there being back-up rollers B1, B2 and B3to support the tube form as it is impressed upon by the said rollersR1-R4. As shown, the rollers R1-R4 and B1-B3 are on spaced and parallelhorizontally disposed and transverse axes.

Back-up roller B1 is disposed over the shaping roller R1 (see FIG. 4)and is characterized by its concaved spool-shape 25 at the center planeof symmetry and conforming to the substantially semi-circular back-upsection 12 of the tube form. Back-up roller B1 has opposite flaring sideflanges that embrace the initial formation of the side sections 14 and15 of the tube form.

Shaping roller R1 (see FIG. 4) is characterized by its convex foldinitiating and shaping perimeter 27 at the center plane of symmetry todepress the tube form wall upwardly at bottom dead center. Shapingroller R1 has opposite concaved side flanges 28 that embrace the initialformation of the lower extremities 21 and 22 of the side sections 14 and15. The perimeters of roller flanges 26 and 28 are closely related so asto capture the tube form therebetween.

Back-up roller B2 is disposed over and intermediate shaping rollers R2and R3 (see FIG. 3) and is characterized by its concaved spool shape 35at the center plane of symmetry and conforming to the substantiallysemi-circular back-up section 12 of the tube form. Back-up roller B2 hasopposite flaring flanges 36, to a lesser extent than that of roller B1,to embrace the formation of the side sections and 15 of the tube form.

Shaping roller R2 (see FIG. 5) is characterized by its convex foldshaping perimeter 37 at the center plane of symmetry to further shapethe tube form wall upwardly along said plane of symmetry. Shaping rollerR2 has opposite concaved side flanges 38 that embrace the lowerextremities 21 and 22 of the side sections 14 and 15. The perimeters ofroller flanges 36 and 38 are somewhat spaced and guide the tube formtherebetween.

Shaping roller R3 (see FIG. 6) is characterized by its convex foldshaping perimeter 47 at the center plane of symmetry to further shapethe tube form wall upwardly along said plane of symmetry. Shaping rollerR3 has opposite concaved side flanges 48, of lesser extent than rollerR2, that embrace the lower extremities 21 and 22 of the side sections 14and 15. The perimeters of roller flanges 36 and 48 are somewhat spacedand guide the tube form therebetween.

Back-up roller B3 (see FIG. 7) is disposed over shaping roller R4 and ischaracterized by its concaved spool-shape 55 at the center plane ofsymmetry and conforming to the substantially semi-circular back-upsection 12 of the tube form. Back-up roller B3 has minimized sideflanges 56 that embrace the side sections 14 and 15 of the tube form.

Shaping roller R4 (see FIG. 7) is characterized by its most sharplyconvexed fold shaping perimeter 57 at the center plane of symmetry tostill further shape the tube form wall along said plane of symmetry.Shaping roller R4 has opposite concaved side flanges 58, of still lesserextent than roller R3, that embrace the lower extremities 21 and 22 ofthe side sections 14 and 15. The perimeters of roller flanges 56 and 58are closely related so as to capture and guide the tube formtherebetween.

The fifth and final collapsing step is performed by a pair of laterallypositioned shaping rollers S1 and S2 disposed at opposite sides of thetube form as it emanates from shaping roller R4 (see FIGS. 8 and 9).Rollers S1 and S2 are to reduce the arcuate cross-section of back-upsection 12 of the tube form, as shown. Accordingly, the rollers S1 andS2 are disposed on spaced and parallel vertical axes and arecharacterized by a concaved spool shape 60 of curvilinear configurationincreasing in curvature from top dead center, each roller, from theinitial full radius of the tube form to the smaller radius of the lowerextremities 21 and 22. The rollers S1 and S2 have top and bottom flanges61 and 62 which are peripherally juxtaposed so as to completely capturethe finally collapsed and deformed tube form, thereby establishing theproduct pipe liner L.

In accordance with this invention, and as best illustrated in FIGS. 8and 9 of the drawings, the tube form of pipe liner L is finallycollapsed onto a rail R disposed between the shaping rollers S1 and S2.The rail R is of a cross-sectional configuration to conform with theinside walls of the side sections 14 and 15 and of the lower extremities21 and 22. Accordingly, and as clearly shown, the final cross-sectionalconfiguration of the pipe liner L is established as required. Inpractice, the rail R has sliding engagement with the tube form and is ofsubstantial longitudinal extent so as to enable a reduction intemperature and firming up while being held in the requiredcross-sectional configuration. Note particularly the hourglasscross-section of the rail R that accommodates the aforementionedcollapsing of the lower extremities 21 and 22, bringing them closertogether in relation to the center plane of symmetry than the upstandinginner walls extending to the bends of fold 16.

From the foregoing, it will be observed that the shaping of the tubeform is gradual and progressive (see FIGS. 3 and 9) and from FIG. 1, itwill be observed that the temperature control is involved, and thepreferred material involved is a thermoplastic. Accordingly, and as bestillustrated in FIG. 3 of the drawings, there are water nozzles 70 thatdispense tempered water so as to maintain the temperature of, forexample 160° F. in order to soften the plastic material and to ensureits bending properties. Nozzles 70 disseminate tempered water into thearea of the shaping rollers R1 through R4 and S1 and S2. Thus, the tubeform is made plastic so as to be collapsed and bent into the desireddeformed condition. Following the final collapsing of the tube form andits sliding engagement on the rail R, the shape enabling temperature ofthe plastic tube form is reduced to ambient by water nozzles 71 thatdispense tempered water at lower temperature so as to cool the finishedpipe liner L to, for example, 70° F., all as shown in FIGS. 1 and 3 ofthe drawings. As shown in FIG. 3, the tempered water is collected in asump or pan 72 for its recirculation as shown in FIG. 1. The coolingmeans C2 reduces the tube form to ambient temperature on or passing intodelivery from rail R.

As shown in FIG. 3 of the drawings, the rollers B1-B3, R1-R4 and S1 andS2 are free to turn on bearings 73 and thereby enable forward motion ofthe tube form through the apparatus as described. However, asthin-walled large diameter pipe liners L are processed, it becomesnecessary with some materials to assist movement of the tube formtherethrough. Accordingly, torque means M in the form of motors M,electrical or hydraulic, provide the assist required (see FIG. 4). It isto be understood that anti-friction bearings 73 are provided withshafting 74, all as is shown throughout the drawings.

From the foregoing, it will be understood that a tubular pipe liner L isprovided that is reduced in cross-sectional configuration so as to bereadily inserted into pipe lines and then reformed to its initiallyextruded cross-sectional configuration, whereby it properly fits intothe pipe line for which it is designed, all as differing circumstancesrequire.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method for producing a deformed pipe liner from an extruded tubular cross-section for insertion into a pipe line and reformation substantially to said extruded tubular cross-section, comprising the steps of:(a) extruding plastic material at a raised temperature into an initial elongated tubular cross-section having a predetermined outside diameter and an elongated axis; (b) collapsing the tubular cross-section, while maintaining the tubular cross-section at a reduced shape enabling deformation temperature above ambient temperature and below said raised temperature, by depressing one side thereof generally diametrically toward an opposite side thereof and toward said axis along a plane of bilateral symmetry on opposite sides of which side sections of the tubular cross-section bend into double-wall configurations; (c) during collapsing, backing the opposite side of the tubular cross-section along the plane of bilateral symmetry, thereby reducing the cross-sectional configuration of said tubular cross-section for insertion into the pipe line and reformation therein substantially to its initially extruded tubular cross-section; (d) disposing a rail along the plane of bilateral symmetry inwardly of the distal ends of said side sections to maintain the liner in the collapsed cross-section; and (e) reducing the temperature of the collapsed cross-section about the rail; whereby, as a result of carrying out steps (b)-(e), the collapsed cross-section is maintained solely by the plastic material of the liner.
 2. A method as set forth in claim 1, wherein the step of collapsing the tubular cross-section includes folding the one side progressively toward the opposite side, thereby progressively dimensionally reducing the tubular cross-section.
 3. A method as set forth in claim 1, wherein the plastic material is a thermosetting polyethylene and wherein the step of extruding is accomplished at a temperature of about 250° F. to 300° F.
 4. A method as set forth in claim 1, including displacing the opposite side sections of said double-wall configurations laterally toward the plane of bilateral symmetry.
 5. A method as set forth in claim 4, wherein collapsing the tubular cross-section includes folding the one side progressively toward the opposite side, thereby progressively dimensionally reducing the tubular cross-section, and progressively displacing said opposite side sections toward one another toward the plane of bilateral symmetry.
 6. A method according to claim 1, wherein collapsing the tubular cross-section includes folding the one side and locating the fold on the side of the axis closest to the opposite side of the tubular cross-section.
 7. A method for producing a deformed pipe liner from a tubular cross-section formed of plastic material for insertion into a pipe line and reformation substantially to said tubular cross-section, comprising the steps of:(a) collapsing the tubular cross-section, while maintaining the tubular cross-section at a shape enabling deformation temperature above ambient temperature, by depressing one side thereof generally diametrically toward an opposite side thereof and toward said axis along a plane of bilateral symmetry on opposite sides of which side sections of the tubular cross-section bend into double-wall configurations; (b) during collapsing, backing the opposite side of the tubular cross-section along the plane of bilateral symmetry and displacing the opposite side sections of said double-wall configurations laterally toward the plane of bilateral symmetry, thereby reducing the cross-sectional configuration of said tubular cross-section for insertion into the pipe line and reformation therein substantially to its initially tubular cross-section; (c) disposing a rail along the plane of bilateral symmetry inwardly of the distal ends of said side sections to maintain the liner in the collapsed cross-section; and (d) reducing the temperature of the collapsed cross-section about the rail; whereby, as a result of steps (a)-(d), the collapsed cross-section is maintained solely by the plastic material of the liner.
 8. A method as set forth in claim 7, wherein the step of collapsing the tubular cross-section includes folding the one side progressively toward the opposite side thereby progressively dimensionally reducing the tubular cross-section.
 9. A method as set forth in claim 7 wherein the step of collapsing the tubular cross-section is at a temperature to prevent elongation of the plastic material.
 10. A method as set forth in claim 7, wherein the step of collapsing the tubular cross-section includes folding the one side progressively toward the opposite side, thereby progressively dimensionally reducing the tubular cross-section, and progressively displacing said opposite side sections toward one another toward the plane of bilateral symmetry.
 11. A method as set forth in claim 10, wherein the step of collapsing the tubular cross-section and displacing the side sections is accomplished at a temperature to prevent elongation of the plastic material.
 12. A method according to claim 7, wherein the step of collapsing the tubular cross-section includes folding the one side and locating the fold on the side of the axis closest to the opposite side of the tubular cross-section.
 13. An apparatus for producing a deformed pipe liner from an extruded tubular cross-section of plastic material comprising:at least one rotatable back-up roller disposed on an axis parallel to an axis of, and generally in opposition to, at least one rotatable shaping roller; the back-up roller having a curved concave spool-shaped periphery centered at a plane of bilateral symmetry and adapted to engage a back-up portion of the tubular cross-section; the shaping roller having a periphery non-complementary in shape to the periphery of said back-up roller and including a curved convex fold initiating and fold shaping peripheral surface at said plane of bilateral symmetry so that when said tubular cross-section passes generally between said back-up and shaping rollers, a deformable portion of the tubular cross-section is depressed diametrically toward the back-up portion thereof and along the plane of bilateral symmetry, so that opposite side sections of the tubular cross-section bend into double-wall configurations with a fold thereof juxtaposed to said opposite back-up portion of the tubular cross-section; such that the cross-sectional configuration of the tubular cross-section is altered and reduced; and a rail disposed generally along said plane of bilateral symmetry downstream of said back-up and shaping rollers and between said side sections.
 14. An apparatus according to claim 13 including means for applying heat to the pipe liner as the back-up and shaping roller deform the pipe liner to its reduced cross-sectional configuration.
 15. An apparatus according to claim 14 wherein said heat applying means applies heat to the liner as the liner is disposed between said side sections.
 16. A method for producing a deformed pipe liner formed of plastic material from a tubular cross-section for insertion into a pipe line and reformation substantially to said tubular cross-section, comprising the steps of:(a) collapsing the tubular cross-section, while maintaining the tubular cross-section at a shape enabling deformation temperature above ambient temperature, by depressing one side thereof generally diametrically toward an opposite side thereof and toward said axis along a plane of bilateral symmetry on opposite sides of which side sections of the tubular cross-section bend into double-wall configurations; (b) during collapsing, backing the opposite side of the tubular cross-section along the plane of bilateral symmetry and displacing the opposite side sections of said double-wall configurations laterally toward the plane of bilateral symmetry, thereby reducing the cross-sectional configuration of said tubular cross-section for insertion into the pipe line and reformation therein substantially to its initially tubular cross-section; (c) disposing a rail along the plane of bilateral symmetry inwardly of the distal ends of said side sections to maintain the liner in the collapsed cross-section; and (d) reducing the temperature of the collapsed cross-section about the rail; whereby, as a result of steps (a)-(d), the collapsed cross-section is maintained without application of means external to the deformed pipe liner.
 17. A method according to claim 16 including the step of extruding the plastic material at a raised temperature above the shape enabling deformation temperature into an initial elongated tubular cross-section having a predetermined outside diameter.
 18. A method according to claim 1 wherein the steps of collapsing and backing the tubular cross-section are performed by engaging rollers against the tubular cross-section, said rail being fixed and non-rotatable, and including the further steps of advancing the liner past the rollers, engaging the liner and the fixed non-rotatable rail, and advancing the liner relative to the fixed non-rotatable rail.
 19. A method according to claim 7 wherein the steps of collapsing and backing the tubular cross-section are performed by engaging rollers against the tubular cross-section, said rail being fixed and non-rotatable, and including the further steps of advancing the liner past the rollers, engaging the liner and the fixed non-rotatable rail, and advancing the liner relative to the fixed non-rotatable rail.
 20. A method according to claim 16 wherein the steps of collapsing and backing the tubular cross-section are performed by engaging rollers against the tubular cross-section, said rail being fixed and non-rotatable, and including the further steps of advancing the liner past the rollers, engaging the liner and the fixed non-rotatable rail, and advancing the liner relative to the fixed non-rotatable rail. 